On the origin and evolution of nest building by passerine birds

The object of this review is to relate nest-building behavior to the origin and early evolution of passerine birds (Order Passeriformes). I present evidence for the hypothesis that the combination of small body size and the ability to place a constructed nest where the bird chooses, helped make possible a vast amount of adaptive radiation. A great diversity of potential habitats especially accessible to small birds was created in the late Tertiary by global climatic changes and by the continuing great evolutionary expansion of flowering plants and insects. Cavity or hole nests (in ground or tree), open-cup nests (outside of holes), and domed nests (with a constructed roof) were all present very early in evolution of the Passeriformes, as indicated by the presence of all three of these basic nest types among the most primitive families of living passerine birds. Secondary specializations of these basic nest types are illustrated in the largest and most successful families of suboscine birds. Nest site and nest form and structure often help characterize the genus, as is exemplified in the suboscines by the ovenbirds (Furnariidae), a large family that builds among the most diverse nests of any family of birds. The domed nest is much more common among passerines than in nan-passerines, and it is especially frequent among the very smallest passerine birds the world over. Each basic type of nest built by passerines has advantages and disadvantages in specific ecological situations, and nest type depends on a balance of multiple factors that involve the nest site, the physical environment, the community, and the size and behavior of the birds.